Preparation And Spin Coherence Of NV Centers In Diamond And Temperature Detection Application

The ever increasing demand in computational power and data transmission rates has inspired researchers to investigate fundamentally new ways to process and communicate information. Among others, physicists explored the usefulness of "non-classical", i.e. quantum mechanical systems of information processing technology, and gave birth to the field of quantum information. Quantum information is a new field of science and technology, which combines quantum physics and information technology. It mainly includes three branches:quantum communication, quantum computing, and quantum precision measurement. Nitrogen-vacancy (NV) center in diamond is a very representative system in solid quantum information technology. Since 1997, when German scientist first measured the optically detected magnetic resonance (ODMR) spectrum of a single NV center, it has increasingly attracted attention around the world, and has found many applications in quantum computing, quantum precision measurement.NV center is a spin defect consisting of a substitutional nitrogen impurity adjacent to a carbon vacancy in diamond. It has excellent properties, such as photostability, biocompatibility, chemical inertness, and long spin coherence and relaxation times at room temperature. These remarkable properties have been explored and used in many applications such as magnetic field sensing, electric field sensing, strain sensing, pressure sensing, thermal sensing, and spin sensing. In this thesis, we first introduce the research background and application of the NV center. Secondly, we report the results of the experimental investigation on its basic spin properties. Thirdly, we introduce the method used in the work for producing the high quality NV centers, which combines the ion implantation technology and electron beam lithography technology. Fourthly, we demonstrate that by using the oxidative etching method, the depth of the NV center can be precisely controlled, and then depth dependence of the coherence times of the NV centers was studied. Finally, we present the results obtained by using the implanted NV center and dynamical decoupling technology, showing a high-sensitivity temperature detection.This thesis is composed of six chapters:In chapter one, we first introduce briefly the basic concept and applications of the quantum information. Then we introduce the fundamental and applications in precision measurement of the NV center, such as magnetic field sensing, thermal sensing, spin sensing. Finally, the content of this thesis is outlined.In chapter two, we first introduce the lattice structure, energy levels, and spectroscopic properties. Then, we introduce the experimental facility, i.e. the scanning confocal microscope system and the microwave and magnetic field system, which are used to find NV center and control the spin of the NV center, respectively. Using the experimental facility, we studied basic properties of the implanted NV centers, such as correlation of the center fluorescence, ODMR spectra, and various coherence behaviors by applying a series of basic microwave pulse sequence to control the spin of the NV center, including Rabi nutation, free induce evolution, spin echo, and spin-lattice relaxation and so on. Moreover, we also introduce dynamical decoupling and electron-electron double resonance method for extending the coherence time, which paves the way for using NV center in high-sensitivity detection.In chapter three, we introduce the methods used for producing NV centers in nanodiamond and bulk diamond. For bulk diamond, we mainly focused on the NV centers implantion methods in high quality diamond, i.e. to improve the proportion of the NV-, to extend its coherence time, and as well using the electron beam lithography to produce NV center array. Then we use the electron beam lithography and ion implantation technology produce long coherence time NV center array, and shallow NV center array and coupled NV centers. This pave the way for using the implanted NV center in quantum information and high-sensitivity detections.In chapter four, we investigated the depth dependence of coherence times of NV centers through precise depth control using oxidative etching at 580℃ in air. By successive nanoscale etching, NV centers could be brought close to the diamond surface step by step, which enabled us to track the evolution of the number of NV centers remaining in the chip and to study the depth dependence of coherence times of NV centers with diamond etching. Our results showed that the coherence times of NV centers in nature isotopic concentration of 13C diamond declined rapidly with the depth reduction in the last about 22±4nm before they finally disappeared, which revealed a critical depth for the influence of a rapid fluctuating surface spin bath, pave the way for studied the diamond surface spin. Moreover, by using the slow etching method combined with low-energy nitrogen implantation, NV centers with depths shallower than the initially implanted depths can be generated, which are preferred for detecting nanoscale external spins with higher sensitivity.In chapter five, we present a high-sensitivity temperature detection using an implanted NV center array and dynamical decoupling in diamond in static magnetic field. It is proved that the coherence time reached 108μs for high order dynamical decoupling, about 14 time the value 7.7μs for thermal Ramsey method. This coherence time corresponded to a thermal sensitivity of 10.1 mK/Hz1/2. We also detected the temperature distribution on the surface of a diamond chip in three different circumstances by using the implanted NV center array with the dynamical decoupling and the thermal sensitivity reached 24 mK/Hz1/2. The experiment implies the feasibility of using implanted NV centers in high-quality diamonds to detect temperatures in biology, chemistry, materials science, and microelectronic systems with high sensitivity and nanoscale resolution.In chapter six, a summarization and a prospect of our work were presented.